Ecg electrode and electrode support

ABSTRACT

An electrically non-conductive back plate for supporting the back of a patient in a supine position comprises on its front face facing the back of the patient a pair or more of ECG electrodes capable of maintaining electrically conductive skin contact with the patient&#39;s back. The pair of ECG electrodes is disposed at a sharp angle with the mean heart vector, in particular so as to form an angle β of about 45°±25° with the projection S of the patient&#39;s spine on the back plate. Also disclosed is an ECG electrode for mounting in a recess of the back plate and an apparatus for treating cardiac arrest by compression of the sternum comprising the back plate.

FIELD OF THE INVENTION

The present invention relates to an ECG electrode and a support on whichthe ECG electrode is mounted, in particular for use in apparatus fortreating sudden cardiac arrest.

BACKGROUND OF THE INVENTION

Sudden cardiac arrest is commonly treated mechanically and/or byelectrical defibrillation. Mechanical treatment may be given manually orby a chest compression apparatus. A number of chest compressionapparatus are known in the art, such as the pneumatically driven LUCAS™mechanical chest compression system (“Lucas™ system”; an apparatus forcompression and physiological in Cardio-Pulmonary Resuscitation, CPR,manufactured by Jolife AB, Lund, Sweden). Specifically the Lucas™ systemcomprises a support structure and a compression unit. The supportstructure includes a back plate for positioning the patient's backposterior to the patient's heart and a front part for positioning aroundthe patient's chest anterior to the heart. The front part has two legs,each having a first end pivotally connected to at least one hinge of thefront part and a second end removably attachable to the back plate. Thefront part is devised to centrally receive the compression unit which isarranged to repeatedly compress the patient's chest when the front partis attached to the back plate. The compression unit comprises apneumatic unit arranged to drive and control compression, an adjustablesuspension unit to which a compression pad is attached, and a means forcontrolling the position of the pad in respect of the patient's chest.Defibrillation may be provided independently of and concomitant.

In deciding when and for how long time to administer compressions to thepatient it is important to measure the electrical activity of the heart.This is accomplished by using a movable ECG apparatus separate of themechanical compression system.

ECG apparatus of this kind comprise a number of ECG electrodes connectedto the apparatus by flexible conductors. Before the start of measurementthe ECG electrodes have to be attached to the chest of the patient in agiven pattern. In a situation of urgency such as one of cardiac arrestthis is time consuming and should be avoided.

EP 459 239 A2 discloses a portable device for sensing cardiac functionand automatically delivering electrical therapy comprising torsionspring operated electrode assemblies.

WO 2004/112683 A1 discloses an electrical means for providingelectrostimulation comprising two electrodes, a front electrode to beapplied on the chest of the patient adjacent to the pad, plate or disc,etc. of the reciprocating means or integrated in the pad, plate or disc,etc., and a rear electrode to be applied to the back of the patientintegrated into the back plate so as to be disposed aboutperpendicularly under the sternum if the patient is resting in a correctposition on the back plate. The electrodes of the means for providingelectrostimulation may be additionally used for picking up ECG signalsand forwarding them to an ECG registration and analysis unit. The ECGsignals obtainable in this manner are however strongly affected by themovement of sternum during compression, which impairs their quality. Thepresent invention seeks to remedy this problem.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide an ECG electrode foruse in apparatus for treating sudden cardiac arrest in a patient bycompression of the sternum, which is easily attached to the skin of thepatient's back.

It is a another object of the invention to provide an ECG electrode foruse in apparatus for treating sudden cardiac arrest by compression ofthe sternum, which is not or only moderately affected by the movement ofsternum.

It is a further object of the invention to provide a support, inparticular a back plate, comprising one or more ECG electrodes in agiven pattern.

Still further objects of the invention will be evident from thefollowing summary of the invention, the description of preferredembodiments thereof illustrated in a drawing, and the appended claims.

SUMMARY OF THE INVENTION

According to the present invention is disclosed a support for supportingthe back of a patient in a supine position comprising a pair or more ofECG electrodes capable of maintaining electrically conductive skincontact with the patient's back. The support is electricallynon-conductive, generally flat and adapted to the portion of the backwhich it is intended to receive for support. It may have, for instance,about rectangular or other symmetric oblong form, in which case the longside of the rectangle or similar extends about perpendicular to aprojection the patient's spine on the support. The support is preferablyof a kind allowing the patient to be centered on the support in a supineposition. In the following the support of the invention will be termed“back plate”; the face of the back plate facing the back of the patientwill be termed “front face”.

According to a first preferred aspect of the invention the back plate iscomprised by an apparatus for treating cardiac arrest by compression ofthe sternum.

According to a second preferred aspect of the invention the lineconnecting the at least one pair of the one or more pairs of ECGelectrodes is disposed at an angle α of 5°±25°, more preferred of5°±15°, with the perpendicular projection on the back plate of the longheart axis of a person of whom the chest is supported by the back plate;the angle α is the one defined by the line/projection in a caudaldirection from their point of intersection. In this application “longheart axis” denotes the direction of a line connecting the center of themitral annulus and the left ventricular apex at the end of the diastolicphase. The direction of the long heart axis in a frontal plane is about40°±20° (H Engblom et al, Am Heart J 2005, 150(3); 507-512). Accordingto the invention it is thus preferred for a line connecting said atleast one pair of the one pair or more of ECG electrodes to be comprisedby an angle β of about 45°±25°, more preferred of about 45°±15°, formedwith the projection S of the spine of a person of which the chest issupported by the back plate. In a generally symmetric back plate theprojection S may be equalled with an imagined short mirror line disposedon the front face of the back plate. The angle β is the one defined bythe line connecting the pair of electrodes and the projection S in acaudal direction from their point of intersection.

According to the present invention is also disclosed an apparatus fortreating cardiac arrest by compression of the sternum, comprising theaforementioned back plate of the invention provided with one pair ormore of the ECG electrodes. It is preferred for the back plate to beeasily mountable on/detachable from the main portion of the apparatusfor treating cardiac arrest.

According to a third preferred aspect of the invention is disclosed anECG electrode capable of being mounted on the back plate so as to facethe patient's back and maintaining electrically conductive skin contact.It is preferred for the ECG electrode to be mounted on the back plate ina manner to make it adapt to slight movements of the patient in respectof the back plate without loosing contact; such movements comprisehorizontal movements but, in particular, perpendicular and skewmovements with an important perpendicular component caused, forinstance, by the patient's sternum being repeatedly compressed toestablish or maintain circulation. It is thus preferred for the ECGelectrode to be displaceable in a horizontal (lateral) direction and/ora vertical direction in respect to the back plate. It is however alsopossible to use electrodes with the back plate that are rigidly mountedin the back plate and thus are not laterally displaceable in respect ofit, for instance needle electrodes such as the electrode disclosed inU.S. Pat. No. 5,509,822, the adaptation for mounting in the back plateis within the easy reach of a person skilled in the art.

According to a fourth preferred aspect the ECG electrode of theinvention is mounted displaceable in a horizontal and/or verticaldirection in a recess provided in the front face of the back plate.

According to a fifth preferred aspect of the invention the ECG electrodecomprises an electrically conductive electrode disk, a resilientlycompressible spring means disposed between the electrode disk and thesupport, and a flexible conducting means for connecting the electrodedisk to an ECG monitoring unit. This arrangement minimizes disturbancesof the ECG signal by body geometry changes caused by the compression ofthe sternum. The electrode of the invention is freely movable in therecess in a direction perpendicular to the support while its lateralmovement is rather restricted. By the force of a spring means the frontface of the electrode is pressed against the skin of the patient's backto provide good electrical contact. Its front face may be provided withelectrical contact enhancing means, such as with an electricallyconducting gel or paste known in the art.

It is preferred for the electrode disk to be supported by anelectrically non-conductive support element, preferably of a rigidpolymer material, disposed between the electrode disk and the springelement. Preferably the support element is integral with the electrodedisk. The compressible spring means may be a coil, a disc of a resilientfoam such as polyurethane foam, a hollow rubber ring or similar. Theelectrode disk, the support element and/or their combination preferablycomprise a cylindrical portion or are substantially cylindrical.

The recess for mounting of the electrode of the invention on the supportis disposed on an essentially flat face thereof and has a formpreferably allowing the electrode to be fully inserted into the recessagainst the resilient force of the spring means which, with their oneend, abut the bottom of the recess. It is preferred that, in a non-loadbearing state, the electrode disk extends from the recess for a shortdistance. It is preferred for the circumference of the recess and of theelectrode disk, the support element, and the combination of electrodedisk and support element to be of similar form and diameter similar soas to provide guidance by the side walls of the recess for the movementof the electrode with little play.

According to a sixth preferred aspect of the invention is disclosed anECG electrode for mounting on a support, in particular the back plate ofthe invention, capable of lateral displacement in regard of the support.

The invention will now be explained in more detail by reference topreferred embodiments illustrated by a rough drawing.

DESCRIPTION OF THE FIGURES

In the attached drawing is shown in:

FIG. 1 a a patient resting with his transparently shown trunk in asupine position on a back plate pertaining to an apparatus for treatingcardiac arrest by compression of the sternum, in a perspective view;

FIG. 1 b the patient and the back plate of FIG. 1 a, with the remainderof the apparatus mounted to the back plate, in the same view;

FIG. 2 an ECG electrode of the invention, mounted on a support, in aunrestrained condition and in a sectional view;

FIG. 3 the ECG electrode of FIG. 2, in the same view but in a restrainedcondition with the back of a patient resting un the support;

FIG. 4 the back plate of FIGS. 1-3, with the trunk of the patient showntransparent and provided with a first and a second pair of ECGelectrodes and their disposition in regard of a positioning grid, in atop view;

FIG. 5 the chest portion of the patient resting on the back plate, withthe first electrode pair of FIG. 4 and electric heart vector shownprojected on the back plate, in an oblique lateral view;

FIG. 6 a an electrocardiogram obtained by recording the ECG signal ofthe first electrode pair of FIG. 4;

FIG. 6 b an electrocardiogram obtained by recording the ECG signal ofthe second electrode pair of FIG. 4;

FIG. 6 c an electrocardiogram obtained by recording the ECG signal ofthe third electrode pair of FIG. 4.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 a shows a seemingly lifeless patient in a supine position, thetrunk 500 of whom has been placed on a back plate 100 resting on afloor. All clothing on the trunk has been removed in preparation forresuscitation by a central unit 182 (FIG. 1 b) for compression of thesternum. In FIG. 1 b the remainder of the apparatus is shown in a statemounted to the back plate 100. Mounting is accomplished in the followingmanner: the free ends of curved right 180 and left 181 legs swivelinglyattached by means of joints 184 and 185, respectively, to the centralpneumatic compression unit 182 from which a reciprocating plunger endingin a suction cup 183 extends towards the sternum of the patient aremounted in lateral brackets 154; 158 and 156; 159 of the back plate 100provided with bores 155 for releasable insertion of short shafts (notshown) extending from said free ends. Left” and “right” designatepositions from the patient's perspective. The apparatus, which sharesthe general design of the Lucas™ system, encloses the patient in thesternum region. By a reciprocating movement of the plunger and thesuction cup 183 the patient's chest is compressed periodically. In itstop or apical position the cup 183 abuts the uncompressed chest at thesternum, from which position the compression cycle starts. Thecompressor unit is driven by compressed air in a gas flask (not shown).

On its side facing the patient's back the back plate is provided withtwo ECG electrodes 105 and 132. One of them, electrode 105, is shown ingreater detail in FIGS. 2 and 3.

The cylindrical electrode 105 comprises an electrically conductiveelectrode disk 161 adhesively attached to a non-conductive supportelement 160 of a suitable polymer like polypropene or polycarbonate,which surrounds a central stem 162 extending from and integral with theelectrode disk 161. The electrode disk/support element 161; 160 ismounted in a cylindrical recess 151 in the front face 150 the back plate100, which rests on a floor 170. The diameter of the recess 151 isslightly larger than the diameter of electrode disk/support element 161;160 to allow the displacement of the latter combination in a directionperpendicular to the front face 150. A spring coil 165 is firmlyattached to the rear side of the support element 160 with its one endand to the bottom 152 of the recess 151 at its other. In its unloadedstate shown in FIG. 2 the electrode 105 extends somewhat above the frontface 150 of the back plate 100. In its state loaded by the trunk 500 ofthe patient the front face of the electrode disk 161 is in electricallyconducting contact with the patient's skin 501 and level with the frontface 150 of the back plate 100. The front face of the electrode disk 161may even be pressed slightly into the recess 151 by the weight of thetrunk and the flexible nature of its soft tissues. This loaded state ofthe electrode 102 is shown in FIG. 3. Electrical connection of the ECGelectrode 102 with an ECG unit (not shown) is provided by means of aflexible electrical conductor 166 attached to the electrode stem 162 atits one end, and to a copper wire 167 moulded into the back plate 100 atits other end. The copper wire 167 is coupled to a contact manifold 169(FIG. 4) to which also the corresponding copper wire 168 of the otherelectrode 132 and further electrodes, if any, are coupled. Via themanifold 169 the electrodes 105, 132 can be connected with an ECGmonitoring unit, which can be integrated into, for instance, the centralpneumatic unit 182 for compression of the sternum, or with a separatehand-held ECG monitoring unit or similar. Connection can be physical orwireless.

FIG. 4 illustrates an area for dorsal electrode placement on the frontface of the back plate 100. For easy identification of possibleelectrode positions the area is defined by a grid of squares comprisingten columns in four rows. The squares are consecutively numbered 1-40starting at the left upper corner and ending at the right lower corner.

The importance of correct positioning of the electrode pairs isillustrated in FIGS. 6 a-6 c. While the ECG trace obtained by theelectrode pair 102-135 (FIG. 5 a) disposed on the back of a healthyperson in squares 2 and 35, respectively, of the positioning grid ofFIG. 4 does not contain useful information, the trace obtained by theelectrode pair 105-132 disposed in squares 5 and 32 of the positioninggrid (FIG. 5 b) reflects the sinus rhythm of a normal heartbeat. The ECGtrace of the electrode pair 2/32 occupying the intermediate position102-132 (FIG. 6 c) has a form between the extremes 105-132 and 102-135.An ECG signal obtained by electrode pair 105-132 (FIG. 6 b) thus can beused to monitor the heartbeat of a patient being administeredcompressions of the sternum by the apparatus of FIG. 2.

Useful ECG electrode pair positions on a back plate are comprised by anangle β of about 45°±25°, preferably of about 45°±15°, formed by theline connecting them with the projection S of the spine on the backplate 100 (FIG. 5) or by an angle α of about 40°±25°, preferably ofabout 40°±15°, by the line connecting them with the projection 502 onthe back plate 100 of the long heart axis 501; in this assessment it isunderstood that the position of the heart and thus the direction of thelong heart axis 501 varies between individuals. The angles α and β aremeasured in a caudal direction from the point of intersection of therespective lines.

1. An electrically non-conductive back plate for supporting the back ofa patient in a supine position comprising on its front face facing theback of the patient a pair or more of ECG electrodes capable ofmaintaining electrically conductive skin contact with the patient'sback, wherein at least one pair of the one pair or more of ECGelectrodes is disposed at a sharp angle with the mean heart vector. 2.The back plate of claim 1, wherein a line connecting said at least onepair of the one pair or more of ECG electrodes is comprised by an angleβ of about 45°±25° formed with the projection S of the spine of a personof which the chest is supported by the back plate.
 3. The back plate ofclaim 2, wherein the angle β is about 45°±15°.
 4. The back plate ofclaim 1, comprising an apparatus for treating cardiac arrest bycompression of the sternum.
 5. The back plate of claim 4 of generallyrectangular shape, comprising coupling means at it short sides fordetachably mounting it to the main portion of said apparatus.
 6. Theback plate of claim 1, wherein at least one ECG electrode of said onepair or more of ECG electrodes is mounted in a recess in the front faceof the back plate.
 7. The back plate of claim 1, wherein at all ECGelectrodes of said one pair or more of ECG electrodes are mounted inrecesses in the front face.
 8. The back plate of claim 6, wherein aspring means is disposed in said recess or recesses between the bottomthereof and the ECG electrode(s).
 9. The back plate of claim 8, whereinsaid ECG electrode(s) are displaceable in said recess(es) in a lateraland/or perpendicular direction.
 10. The back plate of claim 6, whereinsaid recess(es) have a form allowing the electrode(s) to be fullyinserted into the recess(es) against the resilient force of the springmeans.
 11. The back plate of claim 6, wherein, in a non-load bearingstate, the electrode(s) extend from the recess(es) by a short distance.12. The back plate of claim 1, wherein said one or more ECG electrodesare connected to a control unit disposed externally of the back plate.13. The back plate of claim 12, wherein connection is via a manifolddisposed in or at the back plate.
 14. The back plate of claim 13,wherein connection between the manifold and the control unit iswireless.
 15. The back plate of claim 14, wherein the control unit isdisposed in the main portion of the apparatus.
 16. An apparatus fortreating cardiac arrest by compression of the sternum, comprising theback plate of claim
 1. 17. An ECG electrode for mounting in a recess ofa support for supporting the back of a patient in a supine position,comprising an electrically conductive electrode disk, a resilientlycompressible spring means disposed between the electrode disk and thesupport, and a flexible conducting means for connecting the electrodedisk to an ECG monitoring unit.
 18. The ECG electrode of claim 17,wherein an electrically non-conductive support element of a rigidpolymer material is integral with the electrode disk.
 19. The ECGelectrode of claim 17, provided on its front face with an electricalcontact enhancing means, such as an electrically conducting gel orpaste.
 20. The ECG electrode of claim 17, wherein the support comprisesan electrically non-conductive back plate for supporting the back of apatient in a supine position comprising on its front face facing theback of the patient a pair or more of ECG electrodes capable ofmaintaining electrically conductive skin contact with the patient'sback.
 21. An ECG electrode for mounting on a back plate of claim 1,wherein the electrode is capable of lateral displacement in regard ofthe support.